The present invention is broadly applicable for processing aluminum clad ferrous substrates to separately recover the aluminum and ferrous components in reusable form. The present invention is particularly applicable, but not necessarily restricted to the processing of bimetal scrap generated in the manufacture of sleeve or shell-type bearings comprising an aluminum or aluminum alloy lining tenaciously bonded to a steel backing strip. Shell-type bearings of the forgoing type and methods for their manufacture are disclosed in the U.S. Pat. Nos. 3,078,563; 3,221,392; 3,732,083 and 3,955,936 which are assigned to the same assignee as the present invention.
In accordance with the typical methods disclosed in the aforementioned patents, an aluminum or selected aluminum alloy is bonded to a hard metal backing strip such as steel by roll-bonding a strip of aluminum to the steel backing or alternatively, by sintering an aluminum alloy in the form of powder particles on a steel backing strip. In either event, the bimetal strip is produced in great lengths in a continuous manner. Usually, the leading end portion and trailing end portion of the bimetallic strip are not up to specification necessitating a discarding thereof. In a roll-bonding operation for example, it is usually necessary to make some adjustments to the roll spacing during the initial run of the strip to achieve adequate bonding and the lead end portion during the process adjustment phase is below optimum standards and is discarded as scrap. The precision and high standards required for such shell-type bearings in some instances requires other portions of the bimetal strip to be relegated to scrap. A continuing problem associated with the manufacture of such bimetallic aluminum-steel bearing materials has been the inability to economically recover the aluminum and steel constituents separately which has detracted from the efficiency and economics in the manufacture of such bearing materials. This problem has been further aggravated by the increased costs of certain of the alloying constituents employed in the aluminum bearing lining including for example, tin, nickel, manganese and the like.
In recognition of this problem, various methods have heretofore been used or proposed for recovering and separating the aluminum and steel backing strip from such bimetallic scrap. For example, a mechanical separation technique as disclosed in British Pat. No. 1,462,751 relying on differential thermal expansion between the aluminum and steel layers has been found commercially inadequate in effecting an economical and efficient separation of the two constituents. Chemical dissociation and electro-deposition techniques, while satisfactory from the standpoint of effecting a relatively pure separation, are far too costly on a commercial basis. The use of a selective melting technique employing a molten salt bath has also been found unsuitable because the aluminum constituents recovered contain substantial iron contamination in amounts of above 1% by weight. Ordinarily, iron is permissible in aluminum for salvage purposes up to a maximum of 0.4% by weight.
The present invention overcomes the problems and disadvantages associated with prior art salvaging techniques of aluminum-steel bimetal scrap by providing an efficient, economical and simple method for separately recovering the aluminum and steel constituents on a commercial scale. In addition, the present method enables recovery of reusable aluminum or aluminum alloy material from such scrap at a substantial energy savings of up to about 90% in comparison to that required to replace the recovered aluminum scrap with primary metals.